The present invention relates generally to semiconductor devices, and more particularly, to a method and apparatus for an optical detector with spectral discrimination using conventional CMOS components.
Detection of ambient light levels is necessary for purposes such as automatic control of artificial light levels. Silicon photodiodes or phototransistors are frequently employed for this purpose, since they are inexpensive and easy to use. In addition, the silicon photodiodes or phototransistors may be part of an integrated circuit.
However, the response of silicon photo detectors does not match that of the human eye. Depending on the light source and its power spectrum, the difference in brightness as perceived by the human eye and a silicon photo detector can vary greatly. As an example, fluorescent lighting has a spectrum that falls largely within the range of the human eye response, while incandescent lighting emits much of its energy in the infrared (IR) region of the spectrum. A simple silicon photo detector can give a response as much as four (4) times greater for incandescent lighting than for fluorescent lighting for a brightness level which is perceived by the human eye to be the same.
Sunlight has a spectrum between those of fluorescent lighting and incandescent lighting. The ratio of infrared emission to visible emission is highest for incandescent lighting, lowest for fluorescent lighting, and medium for sunlight.
Despite the above discussion, silicon photo detectors can be used for measuring light levels as perceived by the human eye. This can be accomplished by placing an optical filter between the light source and the detector. In doing so, the optical filter enables the composite response to mimic that of the human eye. While this is an effective solution, the filter implies additional expense.
A monolithic optical detector for determining spectral content of an incident light includes at least a first and second well in a substrate, the second well formed proximate the first well. The first well is configured to be exposed to incident light and for generating a first photocurrent as a function of the incident light. The second well is configured to be shielded from the incident light and for generating a second photocurrent as a function of the incident light. Lastly, a processing and control unit, responsive to the first and second photocurrents, determines an indication of spectral content of the incident light. A method and device parameter controller are also disclosed.